"I think that sign means the most to me," says Kristen Fortson, in front of the makeshift memorial outside the Johnson Space Center in Houston. Unlike the myriad tributes to the seven fallen astronauts, this simple message was meant for those who work tirelessly - and anonymously - behind the scenes at NASA.

Ms. Fortson, a payload-integration specialist, came here Sunday to gather strength for her first day back at work after the space shuttle Columbia fell from the sky. It's a day she knows will bring a lot of hugs, prayers, and anxiety about the future.

She is one of the 15,000 civil servants and contractors employed at the Johnson Space Center - a small town's worth of people for whom space exploration is a way of life. That common goal makes tragedies such as Saturday's shuttle explosion all the more difficult to cope with, she says. The emotional high of being part of a successful mission makes the trauma of a disastrous one - no matter how rare - doubly devastating.

"I think there is a sense of complacency when you do something over 100 times successfully," says Fortson. "Something like this makes you think, 'Oh yeah. This is rocket science.' "

Indeed, astronauts constitute less than 1 percent of the people who prepare for a mission. The thousands left behind will be expected to continue working on future missions, while grieving with the rest of the country.

What makes it somewhat bearable, they say, is the outpouring of support from around the globe.

"It's been a tremendously difficult last couple of days," says Bob Cabana, the director of flight-crew operations at NASA. "[Saturday] was probably the hardest day of my life."

Pulling him through it was the strong support and tender encouragement of the American people, he says.

That support may come in the form of a stranger's e-mail, a neighbor's visit, or a pastor's lesson. Here at the memorial in front of the Johnson Space Center, people leave tokens of their affection and respect - and wishes for the future.

One letter written in blue crayon reads: "Dear NASA, We are sorry that the ship exploded yesterday. We hope the next ship that goes up is going to be safe."

Catherine Wester looks at the letter and shakes her head. She came today to mourn - but also to celebrate the lives of those at NASA who are still committed to space exploration. "We don't know them, but I hope they know that our hearts go out to them," says Ms. Wester, who laid yellow roses at the memorial.

The rush to help, recover, and explain

Mary Williams's 6-year-old son, Tylin, laid down the first treasure he could find: a green sucker pulled from his pants pocket.

His mother works at NASA, dealing with logistics aboard the international space station - a field that brought her into daily contact with the astronauts. She and her co-workers had been busily preparing for the next shuttle mission, scheduled for March 1, now canceled in the wake of the Columbia disaster.

"We might slow down for a moment, but we're not going to stop," says Ms. Williams. "I mean, we're up there trying to better humanity."

Immediately upon hearing the news, Williams raced into Mission Control to see how she could help. What she remembers most is the deafening silence. "We're in pain," she says. "I don't know how we're going to bounce back, except through each other. We're in meetings all day, fighting it out for what we believe in. But now we need one another."

The shuttle accident comes at a time when NASA budgets have grown increasingly tight - leaving beleaguered workers feeling even more beleaguered.

Some employees who do not want to be identified say the budget cuts are a serious problem at the space agency, and may contribute to further accidents.

But others insist NASA doesn't skimp on safety. "We joke at NASA about having to attend yet another safety briefing," says Russ Fortson, Kristen's husband and an engineer working for NASA. "Yes, we're pushed to be creative, but we're engineers. That's what we do. And if we tell them we can't do it for this price, they go get more money. I don't think this is a budget issue."

'We don't work in a vacuum'

Standing in back of the surging crowd and rocking his 5-month-old girl, Mr. Fortson says it's the small things - like this makeshift memorial - that help him appreciate just how important his work is.

"It makes me realize that we don't work in a vacuum, that our work has international interest. It gives me a feeling of respect and a greater commitment to what we're trying to accomplish," he says, sniffling with emotion on this humid Houston afternoon.

His wife is a bit more pragmatic about the shuttle accident's repercussions.

"We don't know what is going to happen. Last time [after the Challenger explosion in 1986], there were a bunch of layoffs, budget cuts, and programs shut down for years," says Ms. Fortson, finally turning away from the "Stand Strong" sign. "I hate to think selfishly at a time life this, but we are wondering about our jobs."